Plating racks and methods of racking articles for electroplating



Jan. 21, 1958 w. E. BELKE 2,820,757

PLATING RACKS AND METHODS OF RACKING ARTICLES FOR ELECTROPLATING FiledMay 26, 1955 5 Sheets-Sheet l INVENTOR.

Jan. 21, 1958 w. E. BELKE 2,320,757

PLATING RACKS AND METHODS OF RACKING ARTICLES FOR ELECTROPLATING FiledMay 26, 1955 5 Sheets-Sheet 2 Jan. 21, 1958 w. E. BELKE 2,320,757

PLATING RACKS AND METHODS OF RACKING ARTICLES FOR ELECTROPLATING FiledMay 26, 1955 5 SheetsSheet 3 434i: M lililil'lll'b 84 INVENTOR.

Jan. 21, 1958 w. E. BELKE 2,320,757

PLATING RACKS AND METHODS OF RACKING ARTICLES FOR ELECTROPLATING FiledMay 26, 1955 5 Sheets-Sheet 4 o o -'//f o 0 y 0 96 o o V Jan. 21, 1958w. E. BELKE 2,820,757

PLATING RACKS AND METHODS OF RACKING ARTICLES FOR ELECTROPLATING FiledMay 26, 1955 5 Sheets-Sheet 5 IN V EN TOR.

United rates Patent @fice 2,820,757 Patented Jan. 21, 1958 PLATING RACKSAND METHODS OF RACKING ARTICLES FOR ELECTROPLATING William E. Beike,Chicago, 111., assignor to Bclke Manufacturing (10., Qhicago, 11]., acorporation of Illinois The present invention relates to plating racksand methods of racking articles for electroplating, and is'particularlyconcerned with the provision of improved structures and methods formeeting the electroplating requirements of an infinite number ofdiiferent articles, while preserving useful rack parts in classifiedarrangement for use in meeting future requirements.

One of the objects of the invention is the provision of an improvedmethod of assembling rack parts of the type which can be disassembledand reused, in such manner that a low resistance electrical connectionis assured between the rack parts by cutting into the metal of one partwith the other and exposing a new bright surface for effecting theelectrical connection each time the parts are assembled.

Another object of the invention is the provision of an improved methodof assembly which includes the cutting of a new bright surface forengagement between rack parts, in which provision is automatically madefor covering and sealing these clean connecting surfaces against theingress of electrolyte for maintaining good electrical connection andpreventing erosion of the conducting metal. t 1

Another object of the invention is the provision of improved rackstructures including rack sections and rack tips which are adapted tobeso assembled that a new bright conductingsurface is cut for engagementbetween them whenever they are assembled to provide the low electricalresistance connection between the parts everyv time the parts arereassembled. 7

Another object of the invention is the provision of improved rack andtip structures whichare protected against the action of acid throughout,except at the point where the rack hangs and the tip supports articlestobe electroplated and at the connection between the rack and tip, thelatter connection being automatically sealedby assembly of the partsafter cutting and assuring new bright engaging surfaces between the tipand rack.

Another object of 'the invention is the elimination of the methods andstructures of the prior art in which racks have been provided for aninfinite number of types of articles to be electroplated and the rackshave been dis-. carded after useor stored: in such manner that they arenot likely to befound, even if thesame articles areto be electroplatedagain, and the racks have represented a loss because of the lack ofsystem in their assembly and storage.

Another object of the invention is the provision of improvedelectroplating .racks' and methods in which the racks can be assembledafter coating, and disassembled without injury to the partsorinsulation, and having the following advantages:

(1) Damaged tips can be replaced quickly and economically, and thepresent racks can be kept'at full production.

(2) Tips are easily replaced with plating ditferent articles.

different tip designs for (3) Spacing of tips can be changed. X

(4) Spacing of rack members can be changed.

(5) When no longer needed, racks can be disassembled and the partsreused in racks of similar or different des1gn.

(6) Rack parts can be stored systematically in a small fraction of thespace required for assembled racks.

(7) Systematic storage makes any part or tip instantly available andeasy to use.

Another object of the invention is the provision of improved rackassemblies including vertical splines and cross headers in which theheaders and end portions extending at right angles and provided with aplurality of bolt assemblies for the purpose of holding therackassemblies rigidiy rectangular without the necessity for using otherbraces that would interfere with the tips attached to the rack splineswhich extend vertically between the end splines. I I

Other objects and advantages of the invention will be apparent from thefollowing description and the accompanying drawings, in which similarcharacters of reference indicate similar parts throughout the severalviews.

Referring to the drawings accompanying the specification, of which thereare four sheets,

Fig. l is a view in perspective of an electroplating-rack assembly withvarious exemplary plating tips;

Fig. 2 is a sectional view taken on the plane of the line 2-2 of Fig. 1,looking in the direction of the arrows;

Fig. 3 is a sectional view taken on the plane of the line 3-3 of Fig. 1,looking in the direction of the arrows;

Fig. 4 is an exploded view showing the parts of a rack and 'tip for thepurpose of explaining their assembly;

Fig. 5 is a sectional view taken on the plane of the line 55 of Fig. 1,looking in the direction of the arrows;

Fig. 6 is a view in perspective of one of the tip parts; Fig. 7 is aView in perspective of another tip part; Fig. 8 is another view inperspective of a third tip part 7 of the type employed in Fig. 5;

A members of Fig. 9;

Fig. 12 is a side elevational view in partial section of the otherthreaded member of Fig. 5;

Fig. 13 is a view in perspective of a rack assembly employing twin hooksand twin spines;

Fig. 14 is a similar view of a multipie spine assembly;

Fig. 15 is a sectional View taken on the plane of the line 1515 of Fig.13, looking in the direction of the arrows;

Fig. 16 is a view in perspective of a modified form of rack;

Fig. 17 is a similar view of another modification.

Referring to Fig. 1, this is a view in perspective which is exemplary ofan infinite number of rack assemblies,

, which may be made up out of one or more spine memhers 20, and one or amultiplicity of tip members 21, 22, 23 or 24.

The tip members selected are merely exemplary of a few types, of whichthere are an infinite number of forms for meeting an equal number ofelectroplating requireand tips, which is immersed in the electrolyte orsubjected to its fumes, excepting the upper V-shaped hook 26 of the rack20, which hook is electrically connected to the conducting rod on whichit is supported, and excepting the extreme end surfaces 27 of the tipson that side where the tips engage the electroplated articles.

Thus the tips 21 may have the insulation ground ofi at 27 on the bottomand top of the extreme ends of these tips, because they are intended toengage an article by spreading action, being inserted into anapertureorcavity in the article to'eflect an electricalconducting'connection between the rack and article.

In some embodiments of the invention the hook 26 may also be coated,except its lower surface 28, which actually engages the rod, serving asa bus bar.

The rack member 21), which is sometimes called a spine, comprises anelongated metal bar of substantial thickness and width of conductingmetal, such as copper, provided with the hook at one end'and with theinsulating coating 25, and a plurality of cylindrical 'apertures"ex-'tending through the coating and copper for attachment of the varioustypes of tips. n

For example, the tip 21is a round wire spring contact tip employing athreaded copperbolt 29, with a pairlof wire members 30 and 31, whichhave a pair of converging portions 32, arranged on opposite sides of.the shank of the bolt 29, adjacent the head 33. j

' A sheet metal clip 34 has an aperture 35 for passing the shank of thebolt, and has a pair of inwardly extending flanges 36', each of whichhas a groove 37 for embracing the wires 30 and 31 at their convergingportions 32.

A threaded bushing 38may be threaded on'the threaded shank 39, clampingthe wires 30, 31 against the head ,33, and against the clip 34 andeffectively securing themto the bolt. The wires are bent outwardly at 40on each side of the bolt to bring their parallel body portions 41 into aspread condition, and are bent inwardly again'at 42 to provide shouldersthat may engage the body to jb e' electro-plated just outside anaperture, limiting the move: ment of. the body toward the spine 20. V IThe tip is provided with extreme end portions 43 which may be straightand parallel for insertion into the aperture of thesubject, and theadjacent wires 30, 31 are in, each case given an'initial tension awayfrom each other, so that they may be forced together and inserted inthe' aper ture in the subject, spreading resiliently to bring the baresurfaces 27 into engagement with the subject inside said aperture. Y

The bent formations 40, 41, 42 increase the resiliency of this wire tip.The wire tip so far described is ,completely covered with a thick layerof plastic insulation, leaving the bolt shank 39 bare, and leaving thesurfaces 27 bare. l ,ii

Bushing 38 is surrounded with a sealing sleeve 44, which has anoutwardly extending resilient circular'ffiang'e 45, tapering to a thinedge and adapted to engage the insulating'coating 25 on the spine 20, toeffect a liquid and gastight seal, entirely enclosing this side of thespineagainst the acid. f

The threaded shank 39 also supports a tapered cut ting bushing 46,further to be described, which has a tapered surface 47, provided with amultiplicity of sharp V-shaped ridges 48, of the type better shown inFigs. 11 and 12, separated by V-shaped grooves 49.

These ridges hear such a size relation with respect to the aperture'50.in the rack or spine 20, that the ridges cut grooves in the walls of theaperture 50, forming a new, bright electrical conducting surface on boththe bushings 46 and the aperture 50 every time the two parts are as:sembled and the bushing is drawn into the aperture.

The assembly also includes a threaded member or nut 51, having acomplementary threaded bore 52 for engagement with the shank 39, andhaving an external noucircular surface 53 for engagement with a wrench.

The engaging end of the nut 51 has a tapered frustoconical surface 54which engages in theaperture' 50, and is adapted to rotate therein whilecentering the shank39 in the aperture and drawing the cutting bushing 46and the aperture 50 to secure the tip on the rack. r

The cutting bushing 46 does not rotate as its V-shaped cutting edges45'engage in the metal in the aperture 50,,

preventing rotation; but the frusto-conical surface 54 on the nut 51rotates and engages both the metal around vvaperture 50 and theinsulating coating 25 around the of acid.

Securement of the tip,2 1 on the rack 20, by means of the nut 51,automatically secures it against rotation and draws the resilient tipflange 45 of insulating material or resilient composition against theinsulation 25, automatically sealing this side of the assembly at thesame time the cutting bushing 46 is producing new bright cut surfacesfor engagement between the tips.

This occurs every time the parts are reassembled, as they are intendedto be taken apart when their use has been finished, s'othat the'partsmay be stored with other similar parts and used over again by reassemblywith the same or a different rack for new sub ects.

Thus there is'always a clearance at 59 about the shank 39'between thecutting bushing 46 and the nut 51, throughout the-life of the tip, sothat-there is room to take up any wear 'onthe tip or wear in theaperture of the spine, so that the parts may be drawn into tightengagement with each. other; I 1 3 i Referring to Fig. l, the tip 22 hasits partsof exactly I similar' construction, except that the tip has apair of forwardly extending wire pairs 60, held by the same clip 34,bent forwardly-from" the middle portions 32,, and clamped beneath thenut33a. This is'exemplary'of a tip having a multiplicity of wires forsupporting a multi-v plicity-of subjects.

Referring to tip 23-of Fig. 1, this is exemplary of one type of ruggedflat spring tip, the structure of which is shown in-Fig.- 5. '-In thiscase the tip includes a pair of relatively fiat copper springs 61, 62,the central bodies of which are provided with registering apertures 63.-The;bodies of springs '61, 62 are riveted together at 64,--64,-and-formed with the outwardly turned obtuse angles at 65, so -that"their end portions 66 diverge. These end portions may be completelycovered with the plastic'insul'atiomrwhich may be ground 05 wherever thetips araimenaed t'o'have conducting engagement with a subject to beelectroplated. I I

The samec'u'tting bushing 46 may be employed, but itis provided with anon-circular head 67 for engagement with two of the flanges 68 of ametal clip 69, which has an aperture 70 for the screw bolt71.

The clip 69 has oppositelyextending flanges 72, 72 engaging the edges ofthe flat springs 61 and 62, and preventing the hat springs from rotatingrelative to the cuttingbushing, which is to be fixed on the spine 20, aspreviously described.. a H

The screw .bolt'71' extendsinto the threaded bore 73, but it leavessuflicient room in the threaded bore 73 for the shank 74 of anotherscrew bolt without a head but having a kerf 75 in its end. The taperednut 51 is threaded on the shank 74, drawing the parts into tightelectrical conducting relation with the spine 20, as previouslydescribed, and the nut 51 is covered by a similarinsulatingcapm56,sealing this end of the assembly.

The flat sprin'g'tip 23 is again covered over all with insulationn76,terminating in the tapered ,circularlseal ing jflang'e77j, whichjengagesand seals against the insulating coveringes. Referring-to the ruggedflat spring tip 24 of Fig; 1, the structure of this member is showninFigs, '9 to 1 2, and this spring tip being adapted to smartheaviersubjects, it is provided with a twin mountingi clamps the cuttingbushing to thecruciform i For this purpose a p'air' of flatspringnieniber'sfis and "7 9 have their central fiat body portionssecured with a 'pairof rivets 80 to acrucifo'rm supporting member 81,having rivet apertures'82. The cruciforrn'member 81 has its upwardly anddownwardly'e'xtending portions 83 "provided with 'apertur'es8 4, largeenough to receive the each case at a spacing suitable :for causing 91 inthe bushing to register with 'the apertures '90, spine20. H I V Thespring tip 24, is again bent outwardly at an obtuse angle at 92, '92,providing the spreading ends 93. All

parts of the ,tip assembly on the right side of Fig. 9, except theycutting edges 48 of the cutting bushings 86 are covered with theinsulating compound 94, .which terminates about thecutting bushings 'inthe circular, tapered thin sealing flanges 95 for engaging theinsulation 25. J

On the left side of Fig. 9, the construction about its shank may beidentical with that shown in the previous figures. v A

Referring to Fig. 13, this is exemplary of a rack with twin spines andtwin hooks, and the rack includes a pair of the members 20, previouslydescribed, and provided with a multiplicity of apertures 96. These spinemembers are numbered 97 and 98, and they are joined together at thebottom by a cross bar 99, and at the top by a header bar 100.

The header bar 100 has downwardly .turned end portions providing supportfor a pair of pole assemblies passing through the spines and holding therack rigidly rectangular. I

The cross bar 99 may have a single point of securement 101 at each ofits ends of the construction shown in Fig. 15, while theheader bar 100may have a pair of these connections 102 at each of its ends, as shownin Fig. 15. The twin spine rack of Fig. 13 also represents an assemblywhich may be assembledvto meet the requirements of a particularelectroplating subject, and it may be taken apart and its parts storedwith other similar parts for reuse.

For this purpose the cross bar 99 is provided with a cutting bushing103, similar to that illustrated in Fig. 9, but having its reducedthreaded end portion 104 threaded into a threaded bore 105 in the crossbar 99.

The threaded bushing 103 has the same tapered surface 46 with sharpV-shaped cutting edges 48 for engag ing in an aperture 106 in the spines97 or 98, and. the

cross bar 99 with its cutting bushing 103 is covered over all with thesame layer of plastic insulation 25, surrounding a pair of cuttingbushings 103 on the cross head 100, and terminating in the thin taperedresilient circular flange 107, which efiects a sealing engagement withthe insulation 25 on spine 98.

The other side of the assembly with the cutting bushing 103 issubstantially the same except that the threaded shank 108 is driven hometo the end 109 of the threaded bore 110 in cutting bushing 103 by usinga screw driver in the kerf 111.

The shank 103 and cutting bushing 103 represent a rigid unit in eachcase to be drawn into the aperture 106 by means of the same tapered nut51, which is covered by a cap 56 of insulating material.

Any desired type of tip assembly may be secured in any of the apertures96 in the twin spines 97 and 98 for any particular subject. When thework is completed the parts may be disassembled and stored in bins foreach part with similar parts to be selected at will and reassembled fornew subjects.

Fig. 14 is exemplary of a multiple spine installation, having a longercross head 112 and a longer cross bar 113, provided with multipleapertures for receiving the securing members of Fig. 15. This assemblyincludes plicity of apertures 1 18; and for the purpose of SuPp Itingthe articles to be electroplated in a different position,

the central bodiesof the spines 114-117 have'been given a degree twistat 119, near the top, and near the bottom.

r This causes all of the fingers of the tips which are attached toextend transversely to the header 112 and the cross bar 113, permittingthe rack assembly to support articles which are longer in the transversedirection, but which are located close together on the rack.

The structure of the tips and of the racks which support the tips mayvary infinitely to meet the requirements ofan equal number of articlesto be electroplated; but the method of using these structures includesthe following steps: I 1

The rack member is provided with a body covering over all with a layerof plastic insulation, but having one or more through apertures. The tipis in every case secured to a tapered cutting bushing which isinsertable into oneof said apertures and which has sharp V-shapedcutting edges that cut into the metal of the aperture and expose new V-shaped surfaces for engagement with the bushing supporting the tip.

The metal of the aperture may be said to flow as the tapered bushingprogresses into it with its sharp edges, and the tapered bushing becomesfixed against rotation, while producing this new bright, bare copperconducting surface engaging the bushing.

The rack of Fig. 14 has its cross head 112 provided with downwardlyturned ends for supporting a pair of bolt assemblies passing through thesplines; and this structure also holds the rack rigidly rectangularwithout other bracing.

The bushing includes a threaded bore for receiving a threaded shank onwhich there is mounted a threaded nut having a tapered portion engagingin the aperture, centering the threaded shank and drawing the cuttingbushing into cutting engagement with the aperture.

A tapered nut leaves a threaded portion of the shank protruding forengagement with an insulating cap, threaded thereon and covering the nutwhile engaging the insulating covering on the rack to seal that side ofthe assembly against ingress of acid.

The tip structure on the other side is covered with the same thickplastic insulation, excepting the sharp tapered V-shaped cutting edgeswhich are surrounded with an outwardly extending circular, thin flexibleresilient flange that resiliently engages the insulation on that sideand seals the assembly on that side against ingress of acid.

Thus a connection of high electrical conductivity and rigidity isprovided although the parts may be disassembled, stored and reused overand over again. An ample clearance is provided between the end of thetapered nut and the end of the cutting bushing, so that there is alwaysroom for them to be drawn into tight engagement in the same or otheraperture in a supporting rack.

It will thus be observed that I have invented an improved electroplatingrack structure and improved methods of assembly, whereby an acid-tightseal is automatically provided, surrounding and enclosing newly cut andbri ht engaging surfaces between the parts of the tip and the parts ofthe supporting spine.

My method has the advantage that damaged tips can be replaced quicklyand economically, and the racks can be kept at full production.

Fig. 16 is a view in perspective of another form of rack having a spine125, as previously described, with a hook 130. Spine has a plurality ofT bars 127, 12,8, 129; and each T bar may comprise a flat bar of metalhaving a bracket plate 126 integrally welded thereto and provided withupper and lower apertures for bolts 1.3 1, 132, which pass through thespine 125 and secure the bars 127 rigidly in place.

The T bars 127 and brackets 126 are covered over ent articles.

among? a Referring to- FigI 17; this is another form of 'l' bar .rack inwhich the Tbars:135,,135, an dl13f7 areattached to centralbrackets 138by]weld in g, and;covered=with insulation overall. The T bars are againprovidedwith the bolt assemblies 13 1, 132 passingtthrgugh the spine:and resembling 'in structure the details of Fig. 115,

The bars. 135 137 have -a rightangulartwist adjacent the bracket 138 ineach: case; and this causes the tips 133 to extend horizontally,'thesetips being similar in all respects to the assembly shown in Fig.The right angular twist places the tips inhorizontalpositiongand theprovision of twoboltson the bracketsecurestheT bars rigidly; at rightangles to the spine.

The spacing of the tips can be changed a n drthe 'spacing of the rackmembers can; be changed, andthe tips are easily replaced withdififerenttiptdesigns forplating difi'er- When no longer neededthe:raeksfpa i be disassembled and the parts 'Ieusedin tracksi of similar ordifferent design. The parts may be storedsystematically in bins withsimilar parts in a small fraction ofi the space, required for assembledracks, thus making any'rack or tip put instantly available andIready-tobe used. 7

' All the fore'going advantagesare also realized while automaticallycutting a new brightlconducting surface between the tip and rack-whenltheLparts are assembled, and also effecting automatically. a'liquid-tight seal about the conducting parts of the rack-fand tipconnection.-

While I have illustratedapreferredembodiment'of my invention, manymodifications may be: made without departing from the spirit ,of theinvention, and l do not wish to be limited to the precise details ofconstruction set forth, but desire to avail myself of all changes withinthe scope of the appended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is: 7

1. An electroplating rack, comprising a pair of vertically extendingmetal spines of flat bar shape, each formed with a downwardly openedV-shaped hook at its upper end, and the under surface ofsaid hooks beingbare on the inside to engage a bus baron the inside, each spine having amultiplicity of through bores for attachment of rack tips, and eachspine having a pair of apertures at its upper end below its hook andanother aperture at its lower end, a cross bar carried by the lower endsof the spines and having registering apertures, a U-shaped upper crossbarcarried by the upper ends of said spines and having aperturesregistering with the upper pair of apertures in each spine, all the saidcross bar apertures being threaded, a threaded bushing in each threadedcross bar aperture, said bushing having antannular shoulder engaging thecross bar in each case and having an enlarged cylindrical body with atapered grooved end portion having converging sharp edges bordering itsgrooves, a threaded shank in said bushing, the bushing having a threadedbore for said shank, said shank passing through an aperture in a spineand having a tapered threaded member on the shank engaging the 8 otherside of; the spine; a thick insulation covering over -t azs ws aossabsvs csp iathe aas rmrqsraps sa d-pres baninsifl t s nh uas. an ns acollar rounding each bushing; and having a thin radial flange s o ar1seain ?a ai tt ai rsai e' nsulat s a d an insulating pap ,nutf-having aboretor grotatably enclosingrsaidfthreaded member,-;and having a similarbore threadedflito receive said shankv end,-.to]hold the .cap in sealingengagement with the spineinsulation; the threaded memberdrawinglthetsharptedgespf the bushing into,cutting contact withtheemetalgin the spine apertures and also effecting a tight seal betweenthe thin radial, flange and the spine insulation. ,1

2 ,An, electroplating rack,;.comprisinga ,pair of-verticallyextending'metal, spinesof flat bar shape, each formed with adownwardly-openedV-shaped. hook .atiits upper end, and: the undersurface of said hooks being bare on the inside to engage;atbus bar onthe inside,,each

spinel having a multiplicity of through V bores for. attachment of racktips, and eachspine havinga pair of apertures atits upper end belowits;hook and anotheraperture at itslower end, a crossbar carried by thelower ends of the spines and having registering apertures, a U-shapedupper cross .bar, carried bythe upper endsof said spines "and havingapertures registering withthe upper pair of apertures in each'fspine,all the said cross bar apertures being threaded, a threaded bushing ineach threaded cross 'bar' aperture, said bushing having an annularshoulder engagingthe cross bar in each caseand having an enlargedcylindrical body with atapered grooved end portion having convergingsharp edges bordering its grooves', a threaded shank in said bushing,the bushing having a threadedbore or said,shank,said shank passingthrough an aperture "in a spine and having a taperedthreaded memberonthe, shank engaging the other side of the spine, a thick insplationcovering over the spines andcross bars except in'theapertuies, and saidcross barinsulation-having an insulating collar surrounding each bushingand having a. thin radial flange on each collar sealing against saidspine insulation, and an insulatingcap nut having a bore for rotatablyenclosing said threaded member, and having a similar bore threaded toreceive said shank end, to hold the cap in sealing eugagementwith thespine insulation, the threaded member drawing the sharp edges of thebushing into cutting contact with the metal in the spine apertures andalso efiecting a tight seal between the thin radial flange and the spineinsulation, said cross bars also supporting a

1. AN ELECTROPLATING RACK, COMPRISING A PAIR OF VERTICALLY EXTENDINGMETAL SPINES OF FLAT BAR SHAPE, EACH FORMED WITH A DOWNWARDLY OPENEDV-SHPED HOOK AT ITS UPPER END, AND THE UNDER SURFACE OF SAID HOOKS BEINGBARE ON THE INSIDE TO ENGAGE A BUS BAR ON THE INSIDE, EACH SPINE HAVINGA MULTIPLICITY OF THROUGH BORES FOR ATTACHMENT OF RACK TIPS, AND EACHSPINE HAVING A PAIR OF APERTURES AT ITS UPPER END BELOW ITS HOOK ANDANOTHER APERATURE AT ITS LOWER END, A CROSS BAR CARRIED BY THE LOWERENDS OF THE SPINES AND HAVING REGISTERING APERTURES, A U-SHAPED UPPERCROSS BAR CARRIED BY THE UPPER ENDS OF SAID SPINES AND HAVING APERTURESREGISTERING WITH THE UPPER PAIR OF APERTURES IN EACH SPINE, ALL THE SAIDCROSS BAR APERTURES BEING THREADED, A THREADED BUSHING IN EACH THREADEDCROSS BAR APERTURE, SAID BUSHING HAVING AN ANNULAR SHOULDER ENGAGING THECROSS BAR IN EACH CASE AND HAVING AN ENLARGED CYLINDRICAL BODY WITH ATAPERED GROOVED QEND PORTION HAVING CONVERGING SHARP EDGES BORDERING ITSGROOVES, A THREADED SHANK IN SAID BUSHING, THE BUSING HAVING A THREADEDBORE FOR SAID SHANK, SAID SHANK PASSING THROUGH AN APERTURE IN A SPINEAND HAVING A TAPERED THREADED MEMBER ON THE SHANK ENGAGING THE OTHERSIDE OF THE SPINE, A THICK INSULATION COVERING OVER THE SPINES AND CROSSBARS EXCEPT IN THE APERTURES, AND SAID CROSS BAR INSULATION HAVING ANINSULATING COLLAR SURROUNDING EACH BUSHING AND HAVING A THIN RADIALFLANGE ON EACH COLLAR SEALING AGAINST SAID SPINE INSULATION, AND ANINSLUATING CAP NUT HAVING A BOR EFOR ROTATABLY ENCLOSING SAID THREADEDMEMBER, AND HAVING A SIMILAR BORE THREADED TO RECEIVE SAID SHANK END, TOHOLD THE CAP IN SEALING ENGAGEMENT WITH THE SPINE INSULATION, THETHREADED MEMBER DRAWING THE SHARP EDGES OF THE BUSHING INTO CUT TINGCONTACT WITH THE METAL IN THE SPINE APERTURES AND ALSO EFFECTING A TIGHTSEAL BETWEEN THE THIN RADIAL FLANGE AND THE SPINE INSULATION.